Process for the oxidative bleaching of crude montan wax

ABSTRACT

CRUDE MONTAN WAX, PARTIALLY DERESINIFIED CRUDE MONTAN WAX AND SAPONIFICATION PRODUCTS OF THE SAID WAXES ARE OXIDATVELY BLEACHED IN POWDERED FORM AT A TEMPERATURE IN THE RANGE OF FROM 10 TO 90* C. WITH GASES CONTAINING OXYGEN AND CATALYTIC AMOUNTS OF DINITROGEN TRIOXIDE OR NITROGEN DIOXIDE.

United States Patent *Olh'ce 3,564,032. Patented Feb. 16, 1971 Int. (:1. ciib 3/08 US. Cl. 260-423 6 Claims ABSTRACT OF THE DISCLOSURE Crude montan wax, partially deresinified crude montan Wax and saponification products of the said waxes are oxidatively bleached in powdered form at a temperature in the range of from 10 to 90 C. with gases containing oxygen and catalytic amounts of dinitrogen trioxide or nitrogen dioxide.

The present invention relates to a process for the oxidative bleaching of crude montan wax, partially deresinified crude montan wax or the saponification products of said waxes.

Processes for oxidatively bleaching crude montan wax, which are carried out in the first place to oxidize and remove the dark components and resinous portions, that is to say which are intended to bleach and fine the crude wax, using, for example, chromic acid, nitric acid or hydrogen peroxide in aqueous phase, are being known for a long time. They have all the disadvantage that in the acid oxidation solution the natural wax esters, even under mild conditions, are decomposed to a large extent into montan wax acids and montan wax alcohols, whereby the native character of the crude wax is substantially lost. Attempts have therefore been made to oxidize crude montan wax under non-saponifying conditions, for example with N0, in the molten state, but in this case undesired nitration reactions occur to a considerable extent. In the nitration, oxidation products are obtained but they are not formed as by-products but as follow-up products of the nitration as indicated by Asinger in Chemie und Technologie der Parafiinkohlenwasserstofie" (1956), page 341. Consequently, they represent decomposition products which can no longer be considered raffinates and are scarcely useful.

Numerous processes to oxidize crude montan wax with air or oxygen have been proposed. When the oxidation is carried out under pressure and at high temperatures (for example 180 C.) the crude montan wax can be oxidized but simultaneously an undesired degradation takes place as disclosed, for example, in German Pat. 508,876. If the reaction temperature is reduced to avoid such a degradation and the process is carried out, like the modern paraflin oxidation, at a temperature of about 130 C. or there below, an oxidation does not take place even in the presence of catalysts. In processes of this type crude montan wax appears to have oxidation inhibiting properties as results from experiments of a joint oxidation of crude montan wax and paraffin, described in Brennstofichemie, volume 1 (1920), page 83, and own experiments.

In contradistinction to crude montan wax, pure montan wax is relatively easy to oxidize with air as taught in German Pat. 407,245, but the process is little economical because the production of the highly refined starting product requires very complicated equipment and involves a high loss factor of wax so that all possible advantages of a cheap oxidation with air are by far compensated.

It has now been found that crude montan wax, partially deresinified crude montan wax or the saponification products of the said waxes can surprisingly be bleached oxidatively without pressure at a temperature in the range of from 10 to 90 C. by treating the waxes in powdered form with gases containing oxygen in the presence of gaseous dinitrogen trioxide or nitrogen dioxide. The products obtained substantially preserve their native character as can be seen by the scarcely increased acid number. As compared with the black-brown starting wax they have a light brown, ocher-like color and a very low content of nitrogen compounds. This latter result is particularly surprising because in view of Asinger (10c. cit. page 334), who describes the action of mixtures of oxygen and nitrogen dioxide on paraflins and states that especially good yields of nitration products are obtained, an analogous course of reaction could be expected, that is a high proportion of nitro compounds.

In the process of the invention there can be oxidatively bleached deresinified as well as not deresinified crude montan wax. It is likewise possible, however, to oxidize montan wax soaps obtained by saponification of deresinified or not deresinified crude montain wax with alkali metal hydroxide or ammonium hydroxide or the mixture of montan wax soaps and non-saponifiable matter obtained by saponification, if desired after previous decomposition with mineral acid. When the latter saponification products are used, oxidation products are obtained having a higher acid number than those from the former non modified wax esters, because the wax alcohols set free in the saponification are probably oxidized concurrently.

In the oxidation of the invention the waxes are used in powdered form. Especially when the reaction is carried out in a stretched fluid bed the distribution of particle sizes is of minor importance. The particle size may vary from 10 to 1000 microns or more. With regard to an oxidation as uniform as possible, a too broad range of particle size and too coarse particles should not be used. It has proved especially advantageous to operate with particle sizes in the range of from about 50 to about 400 microns The oxidation of the powdered waxes is carried out at a temperature in the range of from about 10 to 90 C., preferably 30 to C. with gases containing oxygen, preferably air or mixtures of oxygen and air, in the presence of gaseous N 0 or N0 The lower limit of the content of N 0 or N0 in the oxidation gas is about 0.1% by volume while no upper limit exists although it proved advantageous not to exceed a content of 50% by volume since otherwise the proportion of nitration products increases. The preferred range for a rapid and selective oxidation being a concentration of N 0 or N0 in the gas mixture of from about 1 to 10% by volume.

When N0 is used as catalyst the oxidation gases must contain a certain amount of moisture. In general, the normal moisture content of the total system or of the oxidation gas may be sufficient, but it may be advantageous to add to the oxidation gas a small amount of steam, especially to initially accelerate the reaction.

The process of the invention can be carried out in all apparatuses in which a suflicient motion of the wax powder is ensured, for example in rapid mixers. It is especially advantageous, however, to carry out the oxidation according to one of the known fluidization processes. It is possible, for example, to gas the ground wax in a column from below with a catalyst-containing current of air which is so vigorous that a fluid bed forms. The amount of gas required depends on the technical design of the vortex chamber. In order to avoid losses of N0 or N 0 it s suitable to conduct the gas current in a cycle. In this case it is theoretically suflicient to add once the required amount of catalyst. In practice it is necessary, however, to add a small amount of catalyst continuously to compensate for the amount lost with the condensation of the reaction water. The oxygen taken from the cycle gas to oxidize the wax is replenished by supplying According to the reaction temperature the 0 content of the cycle gas in the fluidized bed may be larger or smaller than in the original air-N0 or N 0 mixture. It is advisable to adjust the supply of O in a manner such that the temperature of the fluidized bed does not exceed 75 C. and advantageously 55 C. Higher temperatures shorten the residence time of the powdered wax in the reaction zone, but they promote secondary reactions with the catalyst. The reaction water formed can be removed from the cycle gas by condensation in a gas cooler.

It is likewise possible, of course, to perform the process in continuous manner, for example by connecting in cascades several fluidization columns, but owing to economical reasons the number of reaction chambers is limited and a product having a relatively wide range of oxidation is obtained. A product having an especially uniform degree of oxidation is obtained in a horizontally stretched fluidized bed in which the powdered wax, floating in the gas current in a more or less thick layer, passes a bed of any desired length under such conditions that neither demixing nor remixing becomes possible and that the indivdual wax particles remain for equal periods of time in the reaction zone.

After having blown through air or nitrogen or washed with pure water or water containing a small amount of ammonia, the resin portion may be removed from the oxidation products by a known method, for example the paraflin process in which the resin is precipitated by adding paraffin to the molten wax, or by extraction with a solvent. It is more advantageous, however, to remove the resin from the molten oxidation product by centrifugation, this being possible because the resinous portions modified by the oxidation are incompletely soluble in the molten wax and partly flocculate if the temperature of the melt does not exceed 100 C.

The oxidation products obtained by the process of the invention are especially suitable for the production of wax acids used as starting materials for synthetic ester waxes. The further processing is more economical in that only 30 to 50% by weight of chromic acid are required in the treatment with chromosulfuric acid to be carried out in known manner, calculated on the amount of chromic acid necessary for a similar bleaching effect with a crude montan wax not subjected to a preliminary oxidation.

The following examples serve to illustrate the invention but they are not intended to limit it thereto.

EXAMPLE 1 A glass column having a height of 1 meter and a diameter of 12 centimeters, the bottom of which was closed with a sieve plate, was charged with 2 kilograms of deresinified crude montain wax having an acid number of 25, a saponification number of 88.8, an ester number of 65, a hydroxyl number of 23, a flow point/drop point of 87/ 88 C. and a particle size of less than 500 microns. The column was maintained at 55 C. by means of a heating jacket. A current of air of 55 C. was blown in through the sieve plate by a blower, which current was so strong that a fluid bed formed. About 2000 liters of air were required per hour. The air was aspirated at the head of the tower and passed through a gas cooler to remove condensed water from the air current and reconducted to the blower. After blowing through air for hours there was no change in the wax either in its aspect or in the characteristic numbers. From a cylinder 50 grams of N0 were then added to the gas cycle. After 10 minutes the temperatures rose distinctly. Owing to the large surfaces of radiation of the apparatus and the large amount of recycled gas the increase in temperature was small so that it could be used as a criterion for the beginning of the reaction only and not for the progress of oxidation. After about 30 minutes the originally black-brown powdered wax acquired a lighter color and in the gas cooler reaction water was condensed. After 3 hours of oxidation the wax had a light brown color. It was washed with water containing a small amount of ammonia and dried. The oxidized wax had the following characteristics: acid number 39, saponification number 112, ester number 73, hydroxyl number 17.4, flow point/drop point 87/ 88 C., nitrogen content 0.3%.

In a subsequent treatment with CrO in sulfuric acid solution about 50% of CrO calculated on the wax used, brought about the same bleaching effect as to of CrO with a wax that had not been oxidized with air.

EXAMPLE 2 2 kilograms of a mixture of crude montan wax potassium soap and crude montan wax alcohol, obtained by saponification of crude wax in the melt with an amount of potassium hydroxide corresponding to the saponification number, were treated in powdered form as described in Example 1 at 30 C. with 1500 liters of air per hour in the presence of 2% by volume of N0 The reaction started at once, within 30 minutes the temperature rose to 45 C. and then dropped again. The product was discharged after 60 minutes and washed with water. A light brown powder was obtained having the following characteristics: acid number 49, saponification number 77, flow point/ drop point 84/85 C.

By subsequent oxidation with 70% of CrO calculated on the amount of pre-oxidized product, a wax was obtained having an acid number of 144, whereas a crude wax which had not been subjected to the oxidation with air required to 200% by weight of CrO to yield a product having the same acid member.

What is claimed is:

1. A process for oxidatively bleaching crude montan wax, partially deresinified crude montan wax or saponification products of the said crude waxes, which comprises treating the waxes in powdered form at a temperature in the range of from 10 to 90 C. with oxygen-containing gases in the presence of gaseous dinitrogen trioxide or nitrogen dioxide.

2. The process of claim 1, wherein the waxes used have a particle size in the range of from 10 to 1000 microns.

3. The process of claim 1, wherein the waxes used have a particle size of from 50 to 400 microns.

4. The process of claim 1, wherein the oxygen-containing gases contain at least 0.1% by volume of N 0 or N0 calculated on the total amount of gas.

5. The proces of claim 1, wherein the oxygen-containing gases contain from about 1.0 to 10% by volume of N 0 or N0 calculated on the total amount of gas.

6. The process of claim 1, wherein the reaction is carried out in a fluidized bed or in a stretched fluidized bed.

References Cited UNITED STATES PATENTS 2/ 1957 Hessler 260-423 2/1961 Sentek 260-423 US. Cl. X.R. 260-406 

